1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, more particularly to a front lit LCD apparatus, and a portable electronic device incorporating such a liquid crystal display apparatus.
2. Description of the Related Art
Liquid crystal display apparatuses display characters and/or images by adjusting the amount of transmitted portions of light from a light source. The liquid crystal itself does not emit light, unlike CRT (cathode ray tube) devices, PDP (plasma display) devices, and EL (electroluminescence) devices.
Conventional liquid crystal display apparatuses are generally classified into transmission type liquid crystal display apparatuses and reflection type liquid crystal display apparatuses. A transmission type liquid crystal display apparatus incorporates a light source or xe2x80x9cback lightxe2x80x9d of a planar configuration (e.g., a fluorescent tube or an EL device) provided behind an LCD (liquid crystal display) device.
A reflection type liquid crystal display apparatus has an advantage in that it performs a display function by utilizing ambient light. As a result, a reflection type liquid crystal display apparatus does not require a back light, and consumes relatively small power. Furthermore, reflection type liquid crystal display apparatuses provide improved visibility in very bright conditions (e.g., indirect sunlight) where a transmission type liquid crystal display apparatus or any emission type display device would provide poor visibility. Therefore, portable information terminal devices and mobile computers, which have enjoyed increasing demand in recent years, often employ reflection type liquid crystal displays.
However, a reflection type liquid crystal display apparatus has the following problems: since a reflection type display apparatus utilizes ambient light for display, its display luminance depends on the environment in which it is used. Accordingly, an image that is displayed on a reflection type display apparatus may become totally illegible in the dark, e.g., at night. This becomes particularly problematic for reflection type display apparatuses incorporating a color filter for color display functions because they require even more ambient light than monochrome display apparatuses.
As one solution to the above problem, a semi-transmission type liquid crystal display apparatus has been proposed which incorporates a half mirror as a reflector. However, half mirrors require a complicated manufacturing process. Moreover, since the structure of a half mirror in itself does not make for highly efficient utilization of light, a semi-transmission type liquid crystal display apparatus incorporating a half mirror does not provide excellent display quality.
Accordingly, a reflection type display apparatus has been proposed which employs a means for illuminating a reflection type display device from the front as an auxiliary illumination device in a dark environment.
An example of an auxiliary frontal illumination device is disclosed in Japanese Utility Model Registration No. 3003427. The disclosed illumination device includes an optical guide member which is disposed in front of an object to be illuminated so as to cover the entire face thereof, the optical guide member having a light controlling surface, as well as a cold cathode fluorescent tube disposed at an edge portion of the optical guide member.
Examples of back-lighting techniques are disclosed in Japanese Laid-Open Publication Nos. 6-123884 and 8-68997, for example. The 6-123884 publication discloses an optical guide member including stripe lenses extending in a direction at an angle with respect to the direction in which the pixels of a transmission type display device are arrayed, thereby minimizing the generation of moire fringes.
According to this technique, an image is perceived by a viewer as the illumination light from the back light source travels through the stripe lenses of the optical guide member and the pixels of the transmission type LCD so as to reach the eyes of the viewer. The pitch of the stripe lenses of the optical guide member and the period of the pixels of the transmission type LCD would normally interfere with each other to cause moire fringes. However, by retaining an angle between the stripe lenses of the optical guide member and the pixels of the transmission type LCD, this technique sufficiently shortens the period of the moire fringes to prevent the viewer from perceiving them.
Japanese Laid-Open Publication No. 8-68997 discloses a back light including two prism sheets such that an angle is retained between the direction of the prism grooves provided in two prism sheets and the direction along which pixels of a transmission type display device are arrayed, thereby minimizing the generation of moire fringes.
The illumination light from the back light travels through the two prism sheets and the pixels of the transmission type LCD before it reaches the eyes of a viewer, so that the interference between the periods of these three elements would normally generate moire fringes. According to this technique of retaining an angle between the three elements, the period of the moire fringes is sufficiently shortened to prevent the viewer from perceiving them. According to this structure, the angle between the two prism sheets and the pixel pattern of the transmission type LCD can be independently set within the range of 4xc2x0 to 86xc2x0.
However, various problems may occur when any one of the above-described conventional illumination devices is employed as an illumination device (front light) for a reflection type LCD, as described below.
First, the illumination device disclosed in Japanese Utility Model Registration No. 3003427 is designed to illuminate objects such as drawings, pictures, or printed materials, which are usually unharmed by any moire patterns (moire fringes) emerging due to light interference. If this illumination device is employed as a front light of a reflection type LCD, light interference may occur between the optical guide member and the regular array of pixels of the reflection type LCD, thereby causing moire fringes. In the cases where the optical guide member includes some periodic structure provided thereon, the colored portions (e.g., red (R), blue (B), and green (G)) of a color filter may intensify a xe2x80x9cprism phenomenonxe2x80x9d (under which light beams of red, green, and blue are separately perceived). As a result, the display quality may greatly deteriorate.
Furthermore, while disclosing a technique of leading light onto the object to be illuminated, the 3003427 publication fails to disclose a light controlling portion having any specific shape or structure. The shape and structure of a light controlling portion and location of a light source are important factors for realizing efficient guiding of light.
Now, the mechanism of moire fringe (stripe pattern) generation due to light interference will be briefly explained with respect to the case of employing an illumination device as a front light of a reflection type LCD.
As shown in FIG. 16, illumination light 2213 from a front light (light source) 2200 is reflected from a periodic structure (consisting of concave and convex portions) 2212 formed on an optical guide member 2211; reflected from the pixels of a reflection type LCD 2210; and allowed to pass back through the periodic structure 2212 of the optical guide member 2211. When a viewer observes the reflection type LCD 2210 against ambient light 2214, the ambient light 2214 will pass through the periodic structure 2212 of the optical guide member 2211 and will be reflected from the pixels of the reflection type LCD 2210 so as to pass back through the periodic structure 2212 of the optical guide member 2211.
The above-described structure may be considered as including three Periodic Patterns, namely, two periodic patterns which are defined by the two passages of light back and forth through the periodic structure 2212 of the optical guide member 2211, and one periodic pattern defined by the pixel pattern of the reflection type LCD 2210. Due to overlapping of these three periodic patterns, moire fringes may be generated.
Thus, a front light configuration, in which an optical guide member is disposed in front of a reflection type LCD, may allow moire fringes to be generated due to interference between three different periods. On the other hand, aback light configuration, in which an optical guide member is disposed behind a transmission type LCD, may allow moire fringes to be generated due to interference between two elements, i.e., the periodic structure on the optical guide member and the pixel pattern of the transmission type LCD.
Thus, the mechanism of moire fringe generation differs depending on whether the illumination device is employed as a front light for a reflection type LCD or as a back light for a transmission type LCD. Therefore, using either one of the back lights disclosed in Japanese Laid-Open Publication Nos. 6-123884 and 8-68997 as a front light for a reflection type LCD cannot effectively prevent the generation of moire fringes. Little flexibility will be provided with respect to the angular relationship between the aforementioned periodic structures.
A liquid crystal display apparatus according to the present invention includes: an illumination section having a light source and an optical guide member, and a reflection type LCD having a display region including a plurality of pixels for performing a display function, the optical guide member having first and second principal faces opposite to each other and first and second end faces opposite to each other, wherein the reflection type LCD is disposed on or above the first principal face of the optical guide member, and wherein light from the light source enters the optical guide member at the first end face, exits the optical guide member at the first principal face so as to be incident on the reflection type LCD and reflected therefrom, reenters the optical guide member at the first principal face, and exits the optical guide member at the second principal face toward a viewer.
In one embodiment of the invention, the reflection type LCD includes a plurality of color composite pixels and a color filter layer having a regular array of a plurality of color filters, each of the plurality of color composite pixels including a plurality of color pixels, each of the plurality of color pixels being defined by a corresponding one of the plurality of color filters, the plurality of color pixels having a pitch P1 along a first direction, and the plurality of color composite pixels having a pitch P2 along a second direction, the pitch P1 being smaller than the pitch P2, and the light source being disposed in the vicinity of a side of the display region extending substantially in parallel to the first direction.
In another embodiment of the invention, the light source is disposed so that the viewer is located in a direction of specular reflection to which light emitted from the illumination section is subjected at the reflection type LCD.
In another embodiment of the invention, the light source is disposed near an end of the reflection type LCD where terminals for coupling the reflection type LCD to external display circuitry are provided.
In still another embodiment of the invention, the light source is disposed in the vicinity of the first end face of the optical guide member, and a width t1 of the first end face and a width t2 of the second end face of the optical guide member substantially satisfy t1 greater than t2.
In still another embodiment of the invention, the optical guide member includes a periodic structure formed on the second principal face, the periodic structure including propagation portions and reflection portions alternating along a third direction.
In still another embodiment of the invention, the third direction coincides with neither the first direction nor the second direction.
In still another embodiment of the invention, the third direction constitutes an angle in the range from about 10xc2x0 to about 80xc2x0 with respect to the second direction.
In still another embodiment of the invention, the plurality of color pixels of the reflection type LCD are arrayed in a delta arrangement; and the third direction constitutes an angle in the range from about 10xc2x0 to about 25xc2x0 with respect to the second direction.
In still another embodiment of the invention, the plurality of color pixels of the reflection type LCD are arrayed in a delta arrangement; and the third direction constitutes an angle in the range from about 55xc2x0 to about 80xc2x0 with respect to the second direction.
In still another embodiment of the invention, the plurality of color pixels of the reflection type LCD are arrayed in a stripe arrangement; and the third direction constitutes an angle in the range from about 15xc2x0 to about 75xc2x0 with respect to the second direction.
In still another embodiment of the invention, the optical guide member includes an antireflection element provided on the first principal face.
In still another embodiment of the invention, an effective emission length L3 of the light source and a length L4 of a side of the first principal face of the optical guide member that extends substantially in parallel with the effective emission length L3 of the light source substantially satisfy:
0xe2x89xa6(L3xe2x88x92L4)xe2x89xa630 mm.
In still another embodiment of the invention, a vertical length L1 of the display region of the reflection type LCD and a length L2 of a side of the first principal face of the optical guide member that extends substantially perpendicularly to the effective emission length L3 of the light source substantially satisfy:
0xe2x89xa6(L2xe2x88x92L1)xe2x89xa630 mm.
In still another embodiment of the invention, a light shielding member is disposed corresponding to a connection or transition portion between the optical guide member and the light source.
In another aspect of the invention, there is provided an electronic device incorporating any one of the above liquid crystal display apparatuses.
The present specification employs the following terminology regarding various physical orientations:
As seen from a viewer observing a display screen (or a display region) of a liquid crystal display device from a position that allows the most conventional viewing of the display screen, a direction corresponding to the 12 o""clock direction is defined as the xe2x80x9cupper directionxe2x80x9d; and a direction corresponding to the 6 o""clock direction is defined as the xe2x80x9clower directionxe2x80x9d. Furthermore, the direction extending along the 9 o""clock direction and the 3 o""clock direction is defined as the xe2x80x9chorizontal directionxe2x80x9d of the display region; and the direction extending along the 12 o""clock direction and the 6 o""clock direction is defined as the xe2x80x9cvertical directionxe2x80x9d of the display region. In FIGS. 14A and 14B, for example, arrows 42 and 44 represent the xe2x80x9cupper directionxe2x80x9d and the xe2x80x9clower directionxe2x80x9d, respectively, of display regions 101 and 701. The outgoing light directed toward the viewer is defined as the xe2x80x9cspecular reflection direction.xe2x80x9d
The xe2x80x9cfrontxe2x80x9d or xe2x80x9cfront facexe2x80x9d of a reflection type LCD is defined as any surface of the reflection type LCD facing a viewer. In FIG. 1B, for example, a face 46 defines the front face of a reflection type LCD 101.
An xe2x80x9cendxe2x80x9d or xe2x80x9cend portionxe2x80x9d is defined as a portion formed along the periphery of a display region of a liquid crystal display device that does not substantially contribute to the display function of the liquid crystal display device. In FIG. 1A, for example, a liquid crystal display device 101 has an end portion 103.
A liquid crystal display device according to the present invention includes an illumination section having a light source and an optical guide member, and a reflection type LCD having a display region including a plurality of pixels for performing a display function. The optical guide member includes first and second principal faces opposite to each other, and first and second end faces opposite to each other. The reflection type LCD is disposed on or above the first principal face of the optical guide member, so that the light from the light source enters the optical guide member at its first end face, exits the optical guide member at its first principal face so as to be incident on the reflection type LCD and reflected therefrom, reenters the optical guide member at its first principal face, and exits the optical guide member at its second principal face so as to reach the eyes of a viewer. As a result, the light from the light source can be effectively guided to the reflection type LCD even in a dark environment, so that a clear displayed image can be observed. In a relatively bright environment, a clear displayed image can be observed by utilizing ambient light, without utilizing the light from the light source.
In one embodiment, the reflection type LCD includes a plurality of color composite pixels and a color filter layer having a regular array of a plurality of color filters. Each of the plurality of color composite pixels includes a plurality of color pixels. Each of the plurality of color pixels is defined by a corresponding one of the plurality of color filters, where the plurality of color pixels have a pitch P1 along a first direction, and the plurality of color composite pixels have a pitch P2 along a second direction, the pitch P1 being smaller than the pitch P2. The light source is disposed in the vicinity of the side of the display region extending substantially in parallel to the first direction. As a result, the light emitted from the light source travels along a longer period, i.e., the pitch P2 of the color composite pixels which is longer than the period P1 of the color pixels (e.g., including pixels of red (R), green (G), and blue (B)). Thus, a longer interference period is realized, whereby the density of moire fringes is reduced.
In this connection, it is possible to adopt either a stripe arrangement (FIG. 11) or a delta arrangement (FIG. 12), which are representative structures for periodically arrayed color pixels of an LCD. In a stripe arrangement shown in FIG. 11 where each color pixel of R, G, or B is defined as one third of a square region (and which collectively constitute one full color composite pixel), the color pixels are arrayed with a pitch of P along the horizontal direction and a pitch of 3P along the vertical direction. In a delta arrangement shown in FIG. 12 where each R, G, or B color pixel is defined as a rectangular region, the color pixels are arrayed with a pitch of P along the horizontal direction and a pitch of approximately 2P along the vertical direction.
In the stripe arrangement or delta arrangement, the R, G, and B color pixels are periodically formed along the horizontal direction of the display screen, whereas a periodic structure which is equivalent to about two to three times the horizontal dimension of each color pixel is formed along the vertical direction. Thus, by disposing the light source so that the light emitted from the light source travels along the longer pitch of the color pixels, it becomes possible to reduce the density of moire fringes (occurring due to interference between an image created by the light exiting the optical guide member and the periodic structure defined by the color pixels), thereby improving the display quality of the liquid crystal display apparatus.
In another embodiment, the light source included in the illumination section is disposed so that the viewer is located in a direction of specular reflection of the illumination light (i.e., light emitted from the illumination section) occurring at the reflection type LCD. In other words, the light source is disposed at the upper end of the display region of the reflection type LCD. As a result, the light exiting the optical guide member can be effectively propagated to the viewer.
By disposing the light source near an end of the reflection type LCD where terminals for coupling the reflection type LCD to external display circuitry are provided, greater convenience is provided in an application where the liquid crystal display apparatus is incorporated in an electronic device or the like. The reason is that, since portable electronic information devices are generally required to have a very narrow display region for improved portability, the wiring leads for the driving circuitry and the like of the liquid crystal display apparatus must often be accommodated in a space near the end of the display screen where terminals for coupling the LCD to external display circuitry are provided. Thus, by disposing the light source near such an end of the reflection type LCD where terminals for coupling the LCD to external display circuitry are provided and at a frontal position (i.e., so as to be between the viewer and the reflection type LCD), this space can be conveniently used for accommodating the light source and the like. As a result, it becomes possible to design the liquid crystal display apparatus so as to have a very narrow configuration and improve the portability of the electronic device incorporating such a liquid crystal display apparatus.
In another embodiment, a width t1 of the first end face and a width t2 of the second end face of the optical guide member satisfy t1 greater than t2. As a result, it becomes possible to reduce angle xcex8 1 (FIG. 13) of the outgoing light from the optical guide member with respect to a normal axis 20 of the outgoing face (i.e., first principal face) of the optical guide member, thereby enabling efficient guiding of the light from the light source to an object to be illuminated.
In another embodiment, the optical guide member includes a periodic structure formed on its second principal face, the periodic structure including propagation portions and reflection portions alternating along a third direction. As a result, the light from the light source is propagated through the propagation portions, and the incident light is subjected to total reflection at the reflection portions. Consequently, the light exiting the optical guide member at the outgoing face (i.e., the first principal face) can be brought closer to the normal axis of the first principal face. Thus, the outgoing light can have a uniform luminance distribution, while reducing the amount of light (leak light) exiting the optical guide member at the second principal face toward the viewer, so that the light from the light source is efficiently guided to an object to be illuminated, i.e., the reflection type LCD.
By ensuring that the third direction coincides with neither the first direction nor the second direction it becomes possible to prevent a prismatic action occurring between the periodic structure formed on the optical guide member and a color filter, whereby the display quality is improved.
Specifically, the inventors have found out that, in the case where the direction along which the color pixels of the reflection type LCD are arrayed coincides with the direction of the periods of the periodic structure (e.g., grooves) on the optical guide member, a viewer is likely to observe moire fringes in a prismatic state (due to interference between the periodic structure on the optical guide member and the array of color pixels of the reflection type LCD), whereby the display quality is degraded. This is because the color pixels or layer portions of the same color coincide for one periodic portion. Therefore, by ensuring that the direction along which the color pixels of the reflection type LCD are arrayed does not coincide with the direction of the periods of the periodic structure on the optical guide member, the probability of the color pixels or layer portions of the same color coinciding for one periodic portion is decreased. As a result, any prismatic action can be prevented from occurring when a viewer observes the pixels of the reflection type LCD through the periodic structure on the optical guide member, whereby the display quality is improved.
By ensuring that the third direction constitutes an angle in the range from about 10xc2x0 to 80xc2x0 with respect to the second direction, it becomes possible to prevent moire fringes from being generated due to interference between the periodic structure on the optical guide member, the pattern of the color pixels of the reflection type LCD, and again the periodic structure on the optical guide member.
In another embodiment, arraying the color pixels of the reflection type LCD in a delta arrangement and ensuring that the third direction constitutes an angle in the range from about 10xc2x0 to about 25xc2x0 or in the range from about 55xc2x0 to about 80xc2x0 with respect to the second direction is particularly effective for the prevention of moire fringe generation.
In another embodiment, arraying the color pixels of the reflection type LCD in a stripe arrangement and ensuring that the third direction constitutes an angle in the range from about 15xc2x0 to about 75xc2x0 with respect to the second direction is particularly effective for the prevention of moire fringe generation.
By providing an antireflection element provided on the first principal face of the optical guide member, it becomes possible to reduce the light reflected at the first principal face (i.e., the surface facing the object to be illuminated) of the optical guide member to about 4% or less. As a result, it becomes possible to minimize the generation of fringes (i.e., undulation of relatively bright portions and relatively dark portions) due to the interference between the light from the light source having been subjected to total reflection from the second principal face of the optical guide member (i.e., a light source image) and the light reflected from the first principal face of the optical guide member (i.e., a reflection image).
By ensuring that an effective emission length L3 of the light source and a length L4 of a side of the first end face of the optical guide member that extends substantially in parallel with the effective emission length L3 of the light source substantially satisfy 0xe2x89xa6(L3xe2x88x92L4)xe2x89xa630 mm, it becomes possible to allow the light from the light source to enter efficiently the optical guide member, and provide greater advantages in an application where the liquid crystal display apparatus is incorporated in an electronic device.
By ensuring that a vertical length L1 of the display region of the reflection type LCD and a length L2 of the side of the first principal face of the optical guide member that extends substantially perpendicularly to the effective emission length L3 of the light source substantially satisfy 0xe2x89xa6(L2xe2x88x92L1)xe2x89xa630 mm, it becomes possible to allow the light from the light source to efficiently enter the optical guide member, and provide greater advantages in an application where the liquid crystal display apparatus is incorporated in an electronic device.
By disposing a light shielding member corresponding to a connection or transition portion between the optical guide member and the light source, it becomes possible to shield the leak light from the light source from directly reaching the viewer, thereby improving the display quality.
An electronic device incorporating the above-described liquid crystal display will provide excellent portability with low power consumption and improved visibility and facility of user operation in dark places.
Thus, the invention described herein makes possible the advantages of (1) providing a liquid crystal display apparatus with excellent portability and low power consumption, in which an illumination device is employed as a front light for a reflection type LCD, while preventing the generation of moire fringes and improving the display quality; and (2) providing an electronic device incorporating such a liquid crystal display apparatus.